The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A powertrain includes a torque generative device providing torque to spin an output shaft. A hybrid powertrain utilizes at least two torque generative devices. Hybrid powertrains frequently include a number of methods to utilize the torque generative devices, for example, including a method to select a torque generative device to drive the output shaft, to change the torque generative device driving the output shaft, to select a plurality of torque generative devices to simultaneously drive the output shaft, to utilize one torque generative device to drive another torque generative device, to ground a torque generative device, and to allow the output shaft to spin freely or free-wheel. One exemplary powertrain includes an internal combustion engine and a first and second electric motor, each selectively providing or receiving torque through the powertrain configuration.
Known powertrains include one or more planetary gear sets. Clutch devices known in the art can selectively connect and disconnect various shafts and planetary gear members within the powertrain. As a result of connections and disconnections, various gear ratios and distinct configurations of inputs can be utilized to transmit torque through the resulting powertrain configuration.
Planetary gear sets and clutch devices are utilized within a powertrain as part of a transmission to provide a number of gear states based upon the configuration of the engaged and disengaged clutches. An exemplary two mode hybrid drive transmission includes a first and a second variable gear ratio states and a fixed gear ratio state, wherein the various gear states are selected by engaging and disengaging clutches within the transmissions.
Hydraulic pressure can be utilized to actuate a clutch. In an exemplary clutch utilizing hydraulic pressure in combination with pistons selectively applying force based upon the hydraulic pressure, an exemplary shift between states controlled by a pair of clutches requires that one clutch be unloaded, permitting two shafts that were previously coupled to spin freely of each other, and subsequently that another clutch be loaded, coupling two shafts that were formerly decoupled or free to spin relative to one another. Such hydraulically actuated clutches frequently include clutch plates that are spring loaded to a default decoupled position, and hydraulic pressure applied to an associated piston applies pressure that overcomes the bias of the spring to bring the plates to a coupled position.